Multi-ratio transmission

ABSTRACT

A multi-stage transmission comprising planetary gearsets (P 1 , P 2 , P 3 , P 4 ), shafts and shift elements. The sun gear of gearset (P 1 ) couples drive shaft ( 1 ). The carrier of gearset (P 1 ) couples shaft ( 3 ) which can couple housing (G) via brake ( 03 ), shaft ( 1 ) via clutch ( 13 ), which couples the carrier of gearset (P 4 ), and shaft ( 6 ), via clutch ( 36 ). Shaft ( 6 ) couples the ring gear of gearset (P 2 ) and the sun gears of gearsets (P 3 , P 4 ). Shaft ( 7 ) couples the ring gear of gearset (P 1 ) and the carrier of gearset (P 2 ). The sun gear of set (P 2 ) couples shaft ( 4 ), which can couple housing (G) via brake ( 04 ). The ring gear of gearset (P 3 ) couples shaft ( 5 ), which can couple housing (G) via brake ( 05 ) and output shaft ( 2 ) operatively couples the ring gear of gearset (P 4 ), is connected to the carrier of gearset (P 3 ).

This application is a National Stage completion of PCT/EP2010/062122filed Aug. 19, 2010, which claims priority from German patentapplication serial no. 10 2009 028 671.3 filed Aug. 20, 2009.

FIELD OF THE INVENTION

The present invention relates to a multi step transmission of aplanetary design, in particular an automatic transmission for a motorvehicle.

BACKGROUND OF THE INVENTION

According to the prior art, automatic transmissions, particularly formotor vehicles, comprise planetary gear sets that are shifted usingfriction elements or shift elements such as clutches and brakes, and aretypically connected to a start-up element, such as a hydrodynamic torqueconverter or a fluid coupling, that is subject to a slip effect and isoptionally provided with a lock-up clutch.

Such an automatic transmission is known, for example, from theapplicant's DE 199 49 507 A1, according to which two non-shiftablefront-mounted gear sets are provided on the drive shaft and generate tworotational speeds on the output side, which, in addition to therotational speed of the drive shaft, can be selectively meshed with ashiftable double planetary gear set acting on the output shaft byselective engagement of the shift elements, such that only one of thetwo currently actuated shift elements must be engaged or disengaged toshift from one gear to the next higher or lower gear.

By using five shift elements, seven forward gears are obtained; by usingsix shift elements, nine or ten forward gears are obtained.

Furthermore, a multi step automatic transmission with eight forwardgears and one reverse gear is known from DE 102 13 820 A1, and itcomprises a first input path T1 of a first transmission ratio; an inputpath T2, which features a higher transmission ratio than the input pathT1; a planetary gear set of the Ravigneaux type with four elements,wherein the four elements are placed as a succession of elements in arotational speed diagram as a first element, a second element, a thirdelement and a fourth element: a clutch C-2, which transfers the torqueof the input path T2 to the first element S3; a clutch C-1, whichtransfers the torque of the input path T2 to the fourth element S2; aclutch C-4, which transfers the torque of the input path T1 to the firstelement; a clutch C-3, which transfers the torque of the input path T1to the second element C3; a brake B-1, which produces meshing of thefourth element; a brake B-2, which produces meshing of the secondelement; and a drive element, which is coupled with the third elementS3.

Furthermore, a nine-speed multi step transmission is known from DE 29 36969 A1; it comprises eight shift elements and four gear sets, whereinone gear set serves as a front-mounted gear set and the main gearingincludes a Simpson set and a further gear set serves as reverse gearing.

Additional multi step transmissions are for example known from theapplicant's DE 102005010210 A1 and DE 102006006637 A1.

Automatically shiftable vehicle transmissions of a planetary design, arealready generally described numerous times in the prior art and arecontinually undergoing further development and improvement. Thesetransmissions should have a relatively simple design, in particularrequiring a low number of shift elements, and minimize the need fordouble shifting when sequential shifting is performed, thereby ensuringthat only one shift element is ever switched when shifting is performedin defined groups of gears.

The applicant's document, DE 102008000428.3 that is not yet published,discloses a multi step transmission of a planetary design that includesan input shaft and an output shaft which are disposed in a housing. Theknown transmission includes at least four planetary gear sets which aredesignated, in the following, as the first, second, third, and fourthplanetary gear sets, at least eight rotatable shafts which aredesignated in the following as the drive shaft, output shaft, third,fourth, fifth, sixth, seventh, and eighth shafts, and at least six shiftelements comprising brakes and clutches, whose selective engagementproduces different transmission ratios between the input shaft and theoutput shaft, such that preferably nine forward gears and one reversegear can be realized.

The first and second planetary gear sets, which are preferably designedas minus planetary gear sets, form a shiftable front-mounted gear set,and the third and fourth planetary gear sets form a main gear set.

In the known multi step transmission it is provided that the carriers ofthe first and second planetary gear sets are coupled together via thefourth shaft, which is connected to an element of the main gear set,that the ring gear of the first planetary gear set is coupled with thesun gear of the second planetary gear set via the eighth shaft, which isdetachably connectable to the drive shaft via a first clutch, and thesun gear of the first planetary gear set can be coupled to atransmission housing by means of the third shaft, via a first brake, andis detachably connectable to the drive shaft via a second clutch,wherein the ring gear of the second planetary gear set can be coupledwith a transmission housing by means of the fifth shaft, via a secondbrake. In addition, the seventh shaft is constantly connected to atleast one element of the main gear set, and can be coupled to atransmission housing via a third brake, and the sixth shaft isconstantly connected to at least one further element of the main gearset and is detachably connectable to the drive shaft, via a thirdclutch; the output shaft is constantly connected at least to one furtherelement of the main gear set.

In the known transmission, the fourth shaft is preferably constantlyconnected to the ring gear of the third planetary gear set, the sixthshaft is constantly connected to the ring gear of the fourth planetarygear set and to the carrier of the third planetary gear set, and isdetachably connectable to the drive shaft via the third clutch.Furthermore, the seventh shaft is constantly connected to the sun gearsof the third and fourth planetary gear sets, and can be coupled to atransmission housing via the third brake. In this case, the output driveis produced via the output shaft that is constantly connected to thecarrier of the fourth planetary gear set. Furthermore, the third andfourth planetary gear sets can be combined or reduced to a Ravigneauxset with a common carrier and a common ring gear.

SUMMARY OF THE INVENTION

The objective of the present invention is to propose a multi steptransmission of the initially described type, which has nine forwardgears and at least one reverse gear having a sufficient transmissionratio, in which the design complexity and the overall size, inparticular the overall length and the weight, are optimized, and inwhich efficiency is improved with respect to drag losses and gearinglosses. In addition, in the multi step transmission according to theinvention, minimal support moments should act on the shift elements. Thetransmission, according to the invention, should be particularly suitedfor a front transverse design.

Accordingly, a multi step transmission, according to the invention, of aplanetary design is proposed, which has an input shaft and an outputshaft, which are arranged in a housing. In addition, there are providedat least four planetary gear sets which are designated, in thefollowing, as the first, second, third, and fourth planetary gear sets,eight rotatable shafts which are designated, in the following, as thedrive shaft, output shaft, third, fourth, fifth, sixth, seventh, andeighth shafts, and at least six shift elements comprising brakes andclutches, whose selective engagement produces different transmissionratios between the drive shaft and the output shaft, such thatpreferably nine forward gears and one reverse gear can be realized.

The planetary gear sets, viewed axially, are disposed in the sequence offirst planetary gear set, second planetary gear set, third planetarygear set, fourth planetary gear set, and are preferably designed asminus planetary gear sets.

As is well known, a simple minus planetary gear set comprises a sungear, a ring gear, and a carrier, on which the planetary gears arerotatably supported, the planetary gears meshing with the sun gear andthe ring gear. As a result, when the carrier is fixed, the ring gear hasa direction of rotation that is opposite that of the sun gear. Incontrast, a simple plus planetary gear set comprises a sun gear, a ringgear and a carrier, on which inner and outer planet gears are rotatablysupported, wherein all inner planet gears mesh with the sun gear and allouter planet gears mesh with the ring gear, and each inner planet gearmeshes with only one outer planet gear. As a result, when the carrier isfixed, the ring gear has the same direction of rotation as the sun gear.

According to the preferable embodiment of the invention, the sun gear ofthe first planetary gear set is connected to the drive shaft, which isoperatively connected to the carrier of the fourth planetary gear set,the carrier of the first planetary gear set is connected to the thirdshaft, which can be coupled to a transmission housing via a first brake,is detachably connectable, via a first clutch, to the drive shaft and,via a second clutch, to the sixth shaft, and the sixth shaft isconnected to the ring gear of the second planetary gear set, the sungear of the third planetary gear set and the sun gear of the fourthplanetary gear set.

In addition, the ring gear of the first planetary gear set is connectedto the seventh shaft, which is connected to the carrier of the secondplanetary gear set, the ring gear of the third planetary gear set iscoupled to a transmission housing, via a third brake, the sun gear ofthe second planetary gear set is connected to the fourth shaft, whichcan be coupled with a transmission housing via a second brake, and theoutput shaft, operatively connected to the ring gear of the fourthplanetary gear set, is connected to the carrier of the third planetarygear set.

Preferably, the drive shaft is detachably connectable to the carrier ofthe fourth planetary gear set via the eighth shaft, which is connectedto the carrier of the fourth planetary gear set, and via a third clutch,which detachably connects the eighth shaft to the drive shaft, and theoutput shaft is directly connected to the ring gear of the fourthplanetary gear set.

The embodiment of the multi step transmission, according to theinvention, results in transmission ratios that are particularly suitablefor passenger vehicles, and in a greater overall transmission ratiospread of the multi step transmission, thereby improving drivingsmoothness and significantly reducing fuel consumption.

Furthermore, design complexity is significantly reduced with the multistep transmission, according to the invention, due to a low number ofshift elements. Using the multi step transmission according to theinvention, it is advantageously possible to perform a start-up using ahydrodynamic converter, an external start-up clutch, or any othersuitable external start-up element. It is also conceivable to perform astart-up using a start-up element integrated in the transmission.Preferably, a shift element that is actuated in the first forward gearand in the reverse gear is suitable.

Moreover, the multi step transmission, according to the invention,results in good efficiency in the main drive gears with respect to draglosses and gearing losses.

Furthermore, low moments are present in the shift elements and in theplanetary gear sets of the multi step transmission, therebyadvantageously reducing wear in the multi step transmission. Inaddition, the low moments make it possible to utilize correspondinglylow dimensions, thereby reducing the necessary installation space andrelated costs. Furthermore, the rotational speeds of the shafts, shiftelements, and planetary gear sets are low.

In addition, the transmission, according to the invention, is designedto allow adaptability to different drive train embodiments in terms ofpower flow direction and spatial aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail in the following examples,supported by the attached figures. They show:

FIG. 1: a schematic view of a first preferred embodiment of a multi steptransmission according to the invention;

FIG. 2: an example of a shift pattern for a multi step transmissionaccording to FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a multi step transmission, according to the invention, witha drive shaft 1, an output shaft 2, and four planetary gear sets P1, P2,P3 and P4, which are arranged in a housing G. Planetary gear sets P1,P2, P3 and P4, in the example shown in FIG. 1, are designed as minusplanetary gear sets. According to the invention, at least one planetarygear set can be implemented as a plus planetary gear set, if the carrierand ring gear connection are exchanged and, simultaneously, the value ofthe stationary transmission ratio is increased by 1 in comparison to theembodiment as a minus planetary gear set.

In the embodiment shown, the planetary gear sets, viewed axially, arearranged in the sequence P1, P2, P3 and P4.

As shown in FIG. 1, six shift elements are provided, namely, threebrakes, 03, 04, 05 and three clutches 13, 36 and 18. The spatialdisposition of the shift elements can be arbitrary, and is limited onlyby the dimensions of the outer design. The clutches and the brakes ofthe transmission are preferably implemented as friction shift elementsor lamellar shift elements.

Selective shifting of nine forward gears and one reverse gear can berealized using these shift elements. The multi step transmission,according to the invention, has a total of eight rotatable shafts,namely, the shafts 1, 2, 3, 4, 5, 6, 7 and 8, wherein the drive shaft isthe first shaft, and the output shaft is the second shaft of thetransmission.

The multi step transmission, according to the invention, as shown inFIG. 1, provides that the sun gear of the first planetary gear set P1 isconnected to the drive shaft 1, the carrier of the first planetary gearset P1 is connected to the third shaft 3, which can be coupled to atransmission housing G via a first brake 03, and is detachablyconnectable to the drive shaft 1 via a first clutch 13, and to the sixthshaft 6 via a second clutch 36.

As depicted in FIG. 1, the sixth shaft 6 is connected to the ring gearof the second planetary gear set P2, the sun gear of the third planetarygear set P3 and the sun gear of the fourth planetary gear set P4, andthe drive shaft 1 is detachably connectable to the carrier of the fourthplanetary gear set P4, via the eighth shaft 8, that is connected to thecarrier of the fourth planetary gear set, and via a third clutch 18,which detachably connects the eighth shaft 8 to the drive shaft 1.

According to the invention, the ring gear of the first planetary gearset P1 is connected to the seventh shaft 7, which is connected to thecarrier of the second planetary gear set P2, the ring gear of the thirdplanetary gear set P3 is connected to the fifth shaft 5, which cancoupled to a transmission housing G, via a third brake 05, and the sungear of the second planetary gear set P2 is connected to the fourthshaft 4, which can be coupled to a transmission housing G via the secondbrake 04; the output shaft 2, in the embodiment example shown, isdirectly connected to the carrier of the third planetary gear set P3 andthe ring gear of the fourth planetary gear set P4.

According to the invention, the first clutch 13 and the second clutch36, viewed axially, can be aligned between the first and the secondplanetary gear sets P1, P2, and the third clutch 18, viewed axially inthe direction of the power flow in traction mode, can be aligned afterthe fourth planetary gear set P4.

In addition, the second and third brakes 04, 05, viewed axially, arepreferably arranged side-by-side.

FIG. 2 shows exemplary shift schematics of a multi step transmissionaccording to FIG. 1. Three shift elements are engaged for every gear.The shift schematics shows, by the way of example, the particulartransmission ratios i of the individual gear steps, and, to bedetermined therefrom, the gear increments or step changes phi to thenext higher gear, wherein the value 9.004 is the transmission ratiospread.

Typical values for the stationary transmission ratios of the planetarygear sets P1, P2, P3 and P4 engineered as minus planetary gear sets are:−1.953, −2.191, −2.235 and −2.404, respectively. FIG. 2 shows thatdouble shifting or group shifting is avoided when shifting sequentially,since two adjacent gear steps share two shift elements. It is also shownthat a large transmission ratio spread is attained with small gearincrements.

The first forward gear results from the engagement of the second andthird brakes 04, 05 and the second clutch 36; the second forward gearfrom the engagement of the third brake 05 and the first and secondclutches 13, 36; the third forward gear from the engagement of thesecond and third brakes 04, 05 and the first clutch 13; the fourthforward gear from the engagement of the second and third brakes 04, 05and the third clutch 18; the fifth forward gear from the engagement ofthe second brake 04 and first and third clutches 13, 18; the sixthforward gear, preferably engineered as the direct gear, from theengagement of all the clutches 13, 36, 18; the seventh forward gear fromthe engagement of the second brake 04 and the second and third clutches36, 18; the eighth forward gear from the engagement of the first brake03 and the second and third clutches 36, 18, and that the ninth forwardgear results from the engagement of the first and second brakes 03, 04and the third clutch 18; wherein the reverse gear results from theengagement of all the brakes 03, 04 and 05.

Since the brakes 04 and 05 are engaged in the first forward gear and inthe reverse gear, these shift elements can be used as start-up elements.

According to the invention, different gear increments can also resultfrom the same gear schematics depending on the shift logic, therebymaking it possible to realize an application-specific orvehicle-specific variation.

According to the invention, it is possible to provide additionalfreewheels at each suitable location of the multi stepped transmission,for example, between a shaft and the housing, or possibly to connect twoshafts.

According to the invention, an axle differential and/or a distributordifferential can be disposed on the drive side or on the output side.

Within the scope of an advantageous development, the drive shaft 1 canbe separated from a drive motor, as needed, by a clutch element, whereina hydrodynamic converter, a hydraulic clutch, a dry start-up clutch, awet start-up clutch, a magnetic powder clutch, or a centrifugal clutchcan be used as the clutch element. It is also possible to dispose such astart-up element in the power flow direction after the transmissionwherein, in this case, the drive shaft 1 is continuously connected tothe crankshaft of the engine.

The multi step transmission, according to the invention, also makes itpossible to situate a torsional-vibration damper between the engine andthe transmission.

Within the scope of a further, not represented embodiment of theinvention, a wear-free brake, for instance, a hydraulic or electricretarder or the like, can be disposed on each shaft, preferably on thedrive shaft 1 or the output shaft 2, which is particularly of specialsignificance for use in commercial vehicles. Furthermore, a powertake-off drive can be provided on each shaft, preferably on the driveshaft 1 or the output shaft 2, for driving additional assemblies.

The friction shift elements that are used can be designed as powershiftable clutches or brakes. In particular, force locking clutches orbrakes can be used, for instance, lamellar clutches, band brakes, and/orcone clutches.

A further advantage of the multi step transmission presented here isthat an electric machine can be attached to each shaft as a generatorand/or as an additional drive machine.

Obviously, any structural embodiment, in particular any spatialdisposition of the planetary gear sets and the shift elementsindividually and relative to each other, and insofar as it istechnically expedient, falls under the scope of protection of thepresent claims, without influencing the function of the transmission asspecified in the claims, even if these embodiments are not explicitlyrepresented in the figures or in the description.

REFERENCE CHARACTERS

-   1 first shaft, drive shaft-   2 second shaft, output shaft-   3 third shaft-   4 fourth shaft-   5 fifth shaft-   6 sixth shaft-   7 seventh shaft-   8 eighth shaft-   8′ additional shaft-   03 first brake-   04 second brake-   05 third brake-   13 first clutch-   18 third clutch-   36 second clutch-   P1 first planetary gear set-   P2 second planetary gear set-   P3 third planetary gear set-   P4 fourth planetary gear set-   i transmission ratio-   phi step change-   G housing

The invention claimed is:
 1. A multi step transmission of a planetarydesign for an automatic transmission for a motor vehicle comprising: adrive shaft (1); an output shaft (2); first, second, third and fourthplanetary gear sets (P1, P2, P3, P4) being disposed in a transmissionhousing (G), each of the first, the second, the third, and the fourthplanetary gear sets (P1, P2, P3, P4) comprising a sun gear, a carrierand a ring gear; a third rotatable shaft (3), a fourth rotatable shaft(4), a fifth rotatable shaft (5), a sixth rotatable shaft (6), a seventhrotatable shaft (7), and an eighth rotatable shaft (8); at least sixshift elements (03, 04, 05, 13, 18, 36) comprising a first brake (03), asecond brake (04), a third brake (05), a first clutch (13), a secondclutch (36) and a third clutch (18) whose selected engagement producesdifferent transmission ratios between the drive shaft (1) and the outputshaft (2) such that nine forward gears and one reverse gear can beachieved; wherein the sun gear of the first planetary gear set (P1) isconnected to the drive shaft (1), and the drive shaft (1) is operativelyconnected to the carrier of the fourth planetary gear set (P4); thecarrier of the first planetary gear set (P1) is connected to the thirdshaft (3) which is connectable to the housing (G) via the first brake(03), and the third shaft (3) is connectable to the drive shaft (1), viathe first clutch (13), and to the sixth shaft (6), via the second clutch(36); the sixth shaft (6) is connected to the ring gear of the secondplanetary gear set (P2), the sun gear of the third planetary gear set(P3) and the sun gear of the fourth planetary gear set (P4); the seventhshaft (7) is connected to the ring gear of the first planetary gear set(P1) and the carrier of the second planetary gear set (P2); the sun gearof the second planetary gear set (P2) is connected to the fourth shaft(4) which is connectable to the housing (G) via the second brake (04);the ring gear of the third planetary gear set (P3) is connected to thefifth shaft (5), which is connectable to the housing (G) via the thirdbrake (05); and the output shaft (2) is connected to the ring gear ofthe fourth planetary gear set (P4) and connected to the carrier of thethird planetary gear set (P3).
 2. The multi step transmission accordingto claim 1, wherein the first, the second, the third and the fourthplanetary gear sets (P1, P2, P3, P4) are negative planetary gear sets.3. The multi step transmission according to claim 1, wherein the eighthshaft (8) is connected to the carrier of the fourth planetary gear set(P4) and the drive shaft (1) is detachably connectable to the eighthshaft (8) and the carrier of the fourth planetary gear set (P4), via thethird clutch (18), and the output shaft (2) is connected to the ringgear of the fourth planetary gear set (P4).
 4. The multi steptransmission according to claim 1, wherein the eighth shaft (8) isconnected to the carrier of the fourth planetary gear set (P4) and thedrive shaft (1) is detachably connectable to the eighth shaft (8) andthe carrier of the fourth planetary gear set (P4), via the third clutch(18).
 5. The multi step transmission according to claim 4, wherein afirst forward gear is achieved by engagement of the second and the thirdbrakes (04, 05) and the second clutch (36); a second forward gear isachieved by engagement of the third brake (05) and the first and thesecond clutches (13, 36); a third forward gear is achieved by engagementof the second and the third brakes (04, 05) and the first clutch (13); afourth forward gear is achieved by engagement of the second and thethird brakes (04, 05) and the third clutch (18); a fifth forward gear isachieved by engagement of the second brake (04) and the first and thethird clutches (13, 18); a sixth forward gear is achieved by engagementof the first, the second and the third clutches (13, 36, 18); a seventhforward gear is achieved by engagement of the second brake (04) and thesecond and the third clutches (36, 18); an eighth forward gear isachieved by engagement of the first brake (03) and the second and thethird clutches (36, 18); a ninth forward gear is achieved by engagementof the first and the second brakes (03, 04) and the third clutch (18);and the reverse gear is achieved by engagement of the first, the secondand the third brakes (03, 04, 05).